1. Technical Field
The present invention relates to a clock signal generator generating a clock signal for an information processor, particularly to a clock signal generator suitable for multilevel signal transmission.
2. Related Art
In information processors such as computer systems, binary clock signals (rectangular waves) are used to synchronize the operations of digital ICs. The frequencies of the clock signals in the systems increase (e.g., to several hundred MHz) to enable high-speed operation of the CPUs and, in the CPU chips, the system clock signals are multiplied N (natural number)-fold by PLL (phase locked loop) circuits when they are used.
Meanwhile, in order to achieve power saving in the information processors, supply voltages are continuously changed from 5 volts to 3.3 volts according to the size of the loads on the CPUs, and the frequencies of the operational clock signals in the systems are continuously changed from high to low. For example, JP-A-8-044465 suggests a method for continuously changing an operational clock frequency in a micro processor in accordance with the load on the micro processor and supplying a power supply voltage corresponding to the operational clock frequency to the micro processor, thereby achieving balance between an appropriate operation speed (clock signal frequency) and power consumption reduction.